According to the prior art, it is well known that in order to ensure a shallow base junction during a diffusion process sequence of a bipolar transistor device, a deep P.sup.+ region can not be formed after a base diffusion or implant process, since the base junction depth is a direct function of time and temperature. If the base is already present during the P.sup.+ drive step, the base along with the P.sup.+ region will be driven deep as well, thereby not allowing shallow base depths. Thus, in the prior art, the base implant energy has been limited to approximately 25 KEV. It has been assumed, for certain devices, such as those devices having "overlay geometries", "fishbone geometries", and other geometries requiring close lateral spacing of base and emitter electrodes, that if a low resistance, high conductivity base is required to conduct significant base currents without excessive voltage drops, then the self-alignment feature was not possible, since emitter and base must be defined simultaneously, according to the prior art.
Definition of the emitter and base of a bipolar transistor is typically accomplished with a mask referred to as an emitter-P.sup.+ or "E-P" mask. While the self-alignment feature is desirable because of the superior uniformity of injection and perfect alignment accuracy it provides, it limits the ability to achieve a low resistance P.sup.+ region, since the base must already be diffused or implanted underneath the "E-P" layer. Many methods have tried to minimize the P.sup.+ sheet resistance, such as heavy implant doses of long duration, high energy implants which allow greater depths but which require impractically thick masking layers, and short, high temperature rapid thermal anneals (RTA) process steps, all with little success. For example, utilization of these known methods, which may be very complex, for generating high conductivity P.sup.+ regions, will only yield a P.sup.+ sheet resistance as low as approximately 20 Ohms per square. It would be desirable to minimize this resistance even more.
Thus, there is a current unmet need in the art to be able to manufacture a self-aligned bipolar transistor device having a low resistance, high conductivity P.sup.+ region as well as a low resistance, high conductivity, shallow base region.